The present invention relates to a receiver for receiving and demodulating sound/data information for a number of services transmitting in digital form by means of a packet multiplex system where each packet comprises a header portion and a data portion, the header portion containing an address unique codes for which are allocated to each service with one address allocated to packets whose data portion contains service identification to facilitate the reception of a service in accordance with a user's choice, the data portion of sound/data service packets containing either sound/data information or control information as to the coding scheme for such sound/data information, said receiver comprising a plurality of service recovery devices connected to a common packet bus for the recovery of a plurality of services, a recovery device being adapted to respond at any one time to an address code present in the packet header of packets for a selected service and to recover that service in accordance with the corresponding coding scheme.
Such a receiver is disclosed in FIG. 2 on page 98 of the European Broadcasting Union document SPB 284, 3rd revised version "Television Standards for the Broadcasting Satellite Service Specification of the C/MAC Packet System" December 1984. This figure shows a decoder for a sound service for the above system which is connected to a common packet bus to which other decoders may also be connected, the bus being shown in more detail in FIG. 1 on page 97 of the above document. In a brief description of FIG. 2 appearing on page 82 of the above document it is suggested that some of the decoder functions might be time-shared in receivers having a multiple-decoding facility. Beyond this there is no suggestion as to which functions might be time-shared or how this might be achieved and in view of the Note 4 on page 98 it must be assumed that only one decoder would be provided for all the sound services to be recovered as the other decoders, it is suggested, will be for other types of services such as data broadcasting and subtitling. Such an arrangement would be expensive and inflexible in view of the facilities that would have to be provided in such a sound decoder.